1. Field of the Invention
The present invention relates to systems and methods for controlling electric motors, and more particularly to controlling a power bridge for brushless, direct current (DC) motors for passivation of servos by inhibited motor rotor operation in the event of a failure.
2. Description of Related Art
In mission-critical applications, and in the aviation industry in particular, there is a need to have mechanical systems fail passively. To this end, motion devices such as electric motors are typically required to stop in their last pre-fault position in a locked state to prevent runaway or positional disturbances and the like in mechanical systems during failure.
Three-phase, brushless, direct current (DC) motors employing conventional designs have been used extensively in servo controls for mechanical systems. A typical brushless servo motor includes a permanent magnet rotor and three-phase stator windings. The windings of the servo motor are selectively excited in accordance with the angular position of the motor rotor by opening and closing switching transistors, e.g., a bipolar device, IGBT, FET or the like, to provide switching in a predetermined sequence. The angular position of the motor rotor is detected using a motor position assembly for sensing the position of the motor rotor using multiple, e.g., three position sensors in the form of Hall Effect Sensor (HES) elements disposed at angular spacing of 120 degrees in conventional three-phase designs.
Due to the need to use control electronics to control switching devices, a fault in the motor controller may cause incorrect motor operation, i.e., controller may cause incorrect motor operation, i.e., uncommanded motion. A failure of a commutation position sensor can cause unwanted movement by energizing the windings incorrectly. The use of the Hall Effect elements in the motor position assembly in the brushless DC motor may also fail in an unlocked runaway condition because of the control signals required for commutation. Therefore, in the design of control systems for brushless servo motors, it would be desirable to provide parallel decision-making capabilities for control circuitry associated with driver interfaces for powering the motor, and further provide sensor validation information processing to ensure passivation that inhibits rotation of the motor rotor in the event of system failures.